Recent advancements in recycling technologies for carbon nanotubes and epoxy resins show promise in enhancing their sustainability and reusability. By focusing on innovative bonding techniques, researchers are tackling the complex challenges associated with recycling these strong materials, paving the way for a more efficient circular economy.

Research develops ways to improve the reusability of advanced materials

Two research groups have recently shared their promising approaches to tackling well-known challenges of recycling advanced materials, like carbon nanotubes (CNTs) and epoxy resins. Their work focuses on engineering alternative ways to bond structures together, which could make it easier to reuse them. These innovations could significantly improve their sustainability, helping to reduce waste and use resources more effectively.

Challenges in recycling advanced materials: the struggle for sustainability and reusability

Many advanced materials are held together by covalent bonds, which makes them incredibly strong. This strength poses significant challenges for recycling, resulting in materials that are damaged and less valuable, and limiting their potential for reuse. Additionally, the recycling process for these advanced materials consumes a substantial amount of energy, making it less sustainable and hindering the creation of a circular economy where materials can be reused efficiently.

A solution to recycle CNTs

Currently, the only feasible methods to recycle CNTs are to break them down into small fragments or even powder, or to use heat or chemical treatments to break down the nanotubes. However, both these methods damage their structural integrity.

Researchers at Rice University recently demonstrated that CNT fibres can be recycled without losing their structure or properties. The researchers started with regular CNT fibres and applied a special wet process using a chlorosulfonic acid solution to create what they call solution-spun CNT fibres. These fibres are a sustainable option compared to traditional materials such as metals, polymers, and larger carbon fibres, which can be difficult to recycle. The solution-spun CNT fibres can be returned to their original form using the same solution. When recycled this way, the fibres retain all their original properties, making them as effective as new ones.

A new method to recycle epoxy resins

Epoxy resins are commonly used as highly effective composite adhesives to join and fill different materials like wood, metal, and concrete. However, once these resins harden, they cannot be changed or removed from the materials, which limits their recyclability.

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new method for creating strong materials using what they refer to as ”pseudo-bonds”. Unlike traditional epoxies and other composites that rely on chemical bonds, these new materials work by allowing the molecular chains to entangle in a solution in a fully reversible way.

This new, simple nanocomposite polymer behaves like a tangled ball of yarn; when pulled, it unravels into separate fibres. The polymer consists of polystyrene chains attached to silica particles that are 100 nm in diameter and is both strong and thin. Moreover, it can be disentangled back into its original fibres by adding a solvent. Because there are no chemical bonds to break, these materials can be fully reprocessed.

Reflections by RIVM

Addressing the challenge of recycling advanced materials like CNTs and epoxy resins is crucial. The search for alternative materials that can be efficiently and fully recycled into their original components is commendable. At this moment, many advanced materials are not recyclable at all or only to low grade mixtures of materials. Although recycling is shown here to work at a lab-scale, the road to full scale recycling is a long one due to many hurdles for recycling that are beyond the discussion of the work presented here. Working on alternative materials that can be recycled can significantly contribute to safe and sustainable innovation in the field of advanced materials. More applications of recyclable advanced materials based on engineering pseudo-bonds are likely in development.